Characterization of resistance to multiple fungicides in Botrytis cinerea populations from Asian ginseng in northeastern China

Botrytis cinerea infects ginseng throughout the whole growing season and results in significant economic losses. Fungicides have been the primary strategy in disease control, but frequent applications can increase the risk of fungicide resistance. To determine the resistance of field populations, 76 B. cinerea isolates were collected from 10 ginseng fields in Northeastern China in 2012 and 2013. The sensitivities of these isolates were examined to carbendazim, iprodione, pyrimethanil and azoxystrobin by analyzing mycelial growth inhibition. Almost all test isolates were resistant to at least one fungicide. For example, 27.6 %, 49.9 % and 21.1 % of the population was resistant to one, two or three of four test fungicides, respectively. There was only one isolate that was sensitive to all four fungicides. However, none were simultaneously resistant to all of the four fungicides. Mutations for E198A in the β-tubulin gene and G143A in the cyt b gene were found in all carbendazim- and azoxystrobin-resistant isolates, respectively, indicating a high level of resistance. Various mutations in the bos1 gene were associated with iprodione resistance, among which two combined point mutations, D757N and E369P, could be a novel genotype. Gene structure analysis showed that 50 % of the isolates carried the Bcbi143/144 intron in cyt b, indicating a high inherent risk for the development of G143A-associated resistance to quinone outside inhibitor fungicides. Most resistant isolates did not show reduced compound fitness in mycelial growth, sclerotial and conidial production, aggressiveness and sensitivity to osmotic stress. In conclusion, multi-fungicide resistance of B. cinerea contributed to the inefficiency of current fungicides.